Secondary batteries which are highly applicable to various products and exhibit superior electrical properties such as high energy density, etc. are commonly used not only in portable devices but also in electric vehicles (EVs) or hybrid electric vehicles (HEVs) driven by electrical power sources. The secondary battery is drawing attentions as a new energy source for enhancing environment friendliness and energy efficiency in that the use of fossil fuels can be reduced greatly and no byproduct is generated during energy consumption.
Secondary batteries widely used at the preset include lithium ion batteries, lithium polymer batteries, nickel cadmium batteries, nickel hydrogen batteries, nickel zinc batteries and the like. An operating voltage of the unit secondary battery cell, namely a unit battery cell, is about 2.5V to 4.5V. Therefore, if a higher output voltage is required, a plurality of battery cells may be connected in series to configure a battery pack. In addition, depending on the charge/discharge capacity required for the battery pack, a plurality of battery cells may be connected in parallel to configure a battery pack. Thus, the number of battery cells included in the battery pack may be variously set according to the required output voltage or the demanded charge/discharge capacity.
Meanwhile, when a plurality of battery cells are connected in series or in parallel to configure a battery pack, it is common to configure a battery module composed of at least one battery cell first, and then configure a battery pack by using at least one battery module and adding other components.
In recent years, with regard to the battery cell, a pouch-type secondary battery has been generally used as a lithium polymer battery and. The pouch-type secondary battery is frequently used recently since it has a high energy density per unit weight and volume and easily allows a thin and light design of the battery cell.
A method of manufacturing a battery cell serving as a conventional pouch-type secondary battery will be described below.
First, a positive electrode plate and a negative electrode plate are manufactured, and a separator is interposed therebetween, and then laminated to form an electrode assembly. Then, a plasticizer (DBP) is extracted from the electrode assembly, an electrode tab is welded to an electrode lead of the electrode assembly, and the electrode assembly is included in a pouch case. After the electrode assembly is included in the pouch case, an electrolyte is injected into the pouch case so that the electrode assembly is impregnated with the electrolyte solution. If the electrolyte is injected as described above, the edges of the pouch case are bonded by heat fusion to seal the pouch case.
After that, the battery cell assembled as above is subjected to an aging process for stabilization, and then a charge/discharge process is performed to activate the battery cell. However, during the charge/discharge process, an irreversible reaction occurs between the electrolyte and additives due to the formation of a solid electrolyte interphase (SEI) layer, and gas is generated at this time. The gas inside the pouch case needs to be removed, and if the gas is not removed, a failure occurs in the battery cell. Thus, a degassing process is performed using a battery cell degassing apparatus in order to remove the gas inside the pouch case.
Conventionally, a battery cell degassing apparatus generally removes gas after the battery cell is pressed. In this case, the gas near a center of the pouch case of the battery cell is not removed easily.
In order to solve this problem, rolling is performed using a rolling device before the battery cell is pressed. However, in this case, since the rolling process and the pressing process are performed separately, which lowers the process efficiency and deteriorates the gas removing efficiency.
In addition, the conventional battery cell degassing apparatus may contaminate the exterior of the battery cell since the body of the pouch case may become dirty due to the electrolyte discharged during the degassing process.
Thus, it is required to provide a battery cell degassing apparatus which may increase the gas removal efficiency from the battery cell during the degassing process and minimize the external contamination of the battery cell due to the electrolyte leakage.